Comprehensive Analysis of Lead-Free Perovskite (CsSn_0.5Ge_0.5I₃) Solar Cell: Impact of Active Layer Thickness and Defect Density

Here, we elucidate the influence of active layer thickness and defect density on the photovoltaic performance of lead-free CsSn_0.5Ge_0.5I₃ perovskite solar cells (PSCs). We explained the dependence of FF and J_SC on the perovskite layer thickness and defect density in terms of the extraction rate and generation rate, identifying the role of charge extraction and recombination in the operation of perovskite solar cells. Our finding revealed that when active layer thickness was varied, the best performance was achieved with a thickness of 0.4 µm, resulting in a PCE of 12.79%, open circuit voltage (V_OC) of 0.807 V, FF of 77.42%, and J_SC of 20.47 mA/cm² for the CsSn_0.5Ge_0.5I₃-based PSC. Additionally, the impact of defect density on PSC performance was assessed using the Shockley–Read–Hall recombination model. The degradation of photovoltaic performance was evident as trap density increased, with the PCE dropping from 14.38 to 5.47%. V_OC experienced a significant reduction of 40%, while J_SC and FF showed drops of 25.3% and 14.6%, respectively. The study emphasizes the importance of optimizing active layer thickness and minimizing trap densities to enhance the performance of lead-free PSCs.